1. Technical Field
The present invention is related to a fixed focus imaging lens for forming optical images of subjects onto an imaging element such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor). The present invention is also related to an imaging apparatus provided with the imaging lens that performs photography such as a digital still camera, a cellular telephone with a built in camera, a PDA (Personal Digital Assistant), a smart phone, a tablet type terminal, and a portable gaming device.
2. Background Art
Accompanying the recent spread of personal computers in households, digital still cameras capable of inputting image data such as photographed scenes and portraits into personal computers are rapidly becoming available. In addition, many cellular telephones, smart phones, and tablet type terminals are being equipped with camera modules for inputting images. Imaging elements such as CCD's and CMOS's are employed in these devices having photography functions. Recently, miniaturization of these imaging elements is advancing, and there is demand for miniaturization of the entirety of the photography devices as well as imaging lenses to be mounted thereon. At the same time, the number of pixels in imaging elements is increasing, and there is demand for high resolution and high performance of imaging lenses. Performance corresponding to 5 megapixels or greater, and more preferably 8 megapixels or greater, is desired.
In response to such demands, imaging lenses having a six lens configuration, which is a comparatively large number of lenses, may be considered. For example, Chinese Utility Model Publication No. 202067015 proposes an imaging lens with a six lens configuration, constituted by: a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, a fourth lens, a fifth lens, and a sixth lens, provided in this order from the object side. Japanese Unexamined Patent Publication No. 2004-102083 proposes an imaging lens with a six lens configuration including a first lens group which is positive as a whole, constituted by a first lens having a negative refractive power, a second lens having a positive refractive power, a third lens having a negative refractive power, and a fourth lens having a positive refractive power, and a second lens group having a negative refractive power, provided in this order form the object side. In addition, Japanese Unexamined Patent Publication Nos. 63(1988)-180927, 2(1990)-181714 and 2(1990)-187716 propose imaging lenses that realize high performance variable magnification lenses having six lens configurations, constituted by: a first lens having a negative refractive power, a second lens having a positive refractive power, a third lens having a negative refractive power, a fourth lens having a negative refractive power, a fifth lens, and a sixth lens, provided in this order from the object side.
In addition, wide angle imaging lenses are desired, particularly in imaging devices of cellular telephones, smart phones, and tablet terminals, in which there are often cases in which photographed images are enlarged by a digital zoom function then employed, in order to realize a wider photography range. Japanese Unexamined Patent Publication No. 4(1992)-250408 discloses an imaging lens with a five lens configuration, constituted by: a first lens having a negative refractive power, a second lens having a positive refractive power, a third lens having a negative refractive power, a fourth lens having a positive refractive power, and a fifth lens having a positive refractive power, provided in this order from the object side, in order to realize a wider angle of view.